Aromatic vinyl/isoprene block copolymer, process for the production thereof, and hardenable pressure-sensitive adhesive composition containing the same

ABSTRACT

An aromatic vinyl compound-isoprene block copolymer composition comprising (i) 5-50 wt. % a branched copolymer of the formula: (A-B) n X wherein A is a polymer block of an aromatic vinyl monomer, B is a polymer block of isoprene, and X is a residue of a polyfunctional coupling agent, and (ii) 50-95 wt. % of a diblock copolymer of the formula: A-B wherein A and B are as defined above. This copolymer composition is produced by allowing an aromatic vinyl monomer to contact with an organic lithium initiator to prepare a polymer block A; incorporating isoprene thereto to prepare a diblock copolymer A-B; and then, adding a polyfunctional coupling agent to convert a part of the diblock copolymer A-B to the branched copolymer (A-B) n X. This block copolymer composition is useful for an adhesive or pressure sensitive adhesive composition.

This application is the national phase number 35 U.S.C. §371 of PCTInternational Application No. PCT/JP97/03967 which has an Internationalfiling date of Oct. 30, 1997 which designated the United States ofAmerica.

1. Technical Field

This invention relates to an aromatic vinyl compound-isoprene blockcopolymer composition which is useful as a hot-melt adhesive and otheradhesives, a process for producing the copolymer composition, and anadhesive or pressure sensitive adhesive composition-comprising thecopolymer composition.

2. Background Art

A polystyrene-polyisoprene block copolymer and other block copolymershave widely been used as a base polymer for an adhesive or pressuresensitive adhesive composition. Especially a styrene-isoprene-styreneblock copolymer is known as a base polymer for a hot-melt adhesive.

For the production of disposable diapers, sanitary napkins and the like,a hot-melt adhesive is applied to a thermoplastic sheet or a nonwovenfabric made of a thermoplastic fiber by spiral spraying or other means.As the hot-melt adhesive, those which are applicable at a lowmelt-viscosity and a low temperature are desired with a view topreventing discoloration of adherends such as polyethylene sheet anddeterioration of the hot-melt adhesive. The hot-melt adhesives aregenerally desired to have a melt viscosity of not larger than 5,000 cpsat a temperature of 150° C. However, a hot-melt adhesive composed of astyrene-isoprene block copolymer, which has such a low melt-viscosityupon fusion and exhibits satisfactory peel adhesion and shear adhesionfailure temperature (SAFT), has not been proposed yet.

In U.S. Pat. No. 5,399,627, a styrene-isoprene block copolymercomposition is disclosed, which is produced by a process wherein apolystyrene-polyisoprene diblock copolymer having a minor proportion ofa poybutadiene block bound to a terminal thereof is coupled with acoupling agent having four functionalities, and which is composed of apredominant proportion of the thus-produced copolymer with four branchesand a minor proportion of an unreacted diblock copolymer. This blockcopolymer composition contains only not larger than 29% by weight of theunreacted diblock copolymer, and exhibits a poor peel adhesion when itis applied to a hot-melt adhesive.

In Japanese Unexamined Patent Publication No. H1-266156, astyrene-isoprene block copolymer composition is disclosed, which isproduced by a process wherein a polystyrene-polyisoprene diblockcopolymer is reacted with a tetrafunctional coupling agent in an amountof at least equivalent to an initiator, and which is composed of abranched copolymer with three branches and an unreacted diblockcopolymer. An adhesive made of this block copolymer composition has apoor peel adhesion and a low shear adhesion failure temperature.

Further, in the above-mentioned Japanese patent publication, anotherstyrene-isoprene block copolymer composition is disclosed which iscomposed of a large amount of a polystyrene-polyisoprene diblockcopolymer and a minor amount of a branched copolymer with threebranches. An adhesive of this block copolymer composition has a lowshear adhesion failure temperature.

DISCLOSURE OF INVENTION

An object of the present invention is to provide a block copolymercomposition which is useful as a hot-melt adhesive or other adhesives,which has satisfactory properties required for a hot-melt adhesive,especially has a low melt-viscosity and a low application temperature,and exhibits well balanced and high peel adhesion and shear adhesionfailure temperature; and a process for producing the block copolymercomposition.

Another object of the present invention is to provide an adhesive orpressure sensitive adhesive composition useful as a hot-melt adhesive orother adhesives, which has a low melt-viscosity and a low applicationtemperature, and exhibits well balanced and high peel adhesion and shearadhesion failure temperature.

The inventors conducted extensive research for achieving theabove-mentioned objects, and, found that an adhesive or pressuresensitive adhesive composition comprising a specific styrene-isopreneblock copolymer composition and a tackifier is highly effective as anadhesive attaining the objects, which is easily produced by a processwherein styrene is polymerized by using an organic lithium initiator togive a polymer block A of styrene; isoprene is polymerized in thepresence of the polymer block A to prepare a polymer block B of isopreneand further bind the two polymer blocks A and B together to give an A-Bblock copolymer; and then the A-B block copolymer is allowed to reactwith a predetermined amount of a coupling agent having at least fourfunctionalities, and which comprises 5 to 43.9% by weight of a branchedcopolymer having at least four branches and 56.1 to 95% by weight of anunreacted diblock copolymer. Based on this finding, the presentinvention has been completed.

Thus, in accordance with the present invention, there is provided anaromatic vinyl compound-isoprene block copolymer composition comprising:

(i) 5 to 43.9% by weight of a branched copolymer having at least fourbranches, represented by the following general formula (I):

(A-B)_(n)X  (I)

wherein A is a polymer block of an aromatic vinyl monomer, B is apolymer block of isoprene, X is a residue of a polyfunctional couplingagent having at least four functionalities, and n is an integer of atleast 4, and

(ii) 56.1 to 95% by weight of a diblock copolymer represented by thefollowing general formula (II):

A′-B  (II)

wherein A′ is a polymer block of an aromatic vinyl monomer, which may bethe same as or different from the polymer block A, and B is a polymerblock of isoprene; said block copolymer composition having a weightaverage molecular weight of 10,000 to 500,000.

In accordance with the present invention, there is further provided aprocess for producing the above-mentioned aromatic vinylcompound-isoprene block copolymer which comprises the steps of:

allowing an aromatic vinyl monomer to contact with an organic lithiuminitiator to prepare a polymer block A composed of aromatic vinylmonomer units and having an active terminal exhibiting a polymerizationactivity;

incorporating isoprene to the polymer block A-containing polymerizationsystem whereby an A-B block copolymer is prepared, which has a structuresuch that the polymer block A of aromatic vinyl monomer is directlybonded to a polymer block B composed of isoprene units and having anactive terminal exhibiting a polymerization activity; and then,

adding a coupling agent having at least four functionalities to the A-Bblock copolymer-containing polymerization system to convert 5 to 43.9%by weight of the A-B block copolymer to a branched copolymer having atleast four branches represented by formula (I).

In accordance with the present invention, there is further provided anadhesive or pressure sensitive adhesive composition comprising theabove-mentioned aromatic vinyl compound-isoprene block copolymercomposition and a tackifier.

Best Mode for Carrying Out the Invention

Aromatic vinyl compound-isoprene block copolymer composition

The aromatic vinyl compound-isoprene block copolymer composition of thepresent invention is characterized as comprising the branched copolymerof formula (I) and the diblock copolymer of formula (II).

(1) Branched copolymer

The first ingredient, i.e., the branched copolymer of formula (I)contained in the block copolymer composition of the present invention isa block copolymer having at least four branches which is prepared bycoupling an A-B block copolymer composed of a polymer block A ofaromatic vinyl monomer and a polymer block B of isoprene having anactive terminal exhibiting a polymerization activity, with apolyfunctional coupling agent having at least four functionalities.

The aromatic vinyl monomer used for the preparation of the branchedcopolymer is not particularly limited, and includes, for example,styrene, α-methylstyrene, vinyltoluene and vinylnaphthalene. Of these,styrene is preferable. These aromatic vinyl monomers may be used eitheralone or as a combination of at least two thereof.

The proportion of the aromatic vinyl monomer units in the branchedcopolymer is not particularly limited, but, the content of the polymerblock of aromatic vinyl monomer units in the entire aromatic vinylcompound-isoprene copolymer composition of the present invention ispreferably in the range of 10 to 50% by weight, more preferably 25 to50% by weight and most preferably 35 to 45% by weight, based on thetotal weight of the block copolymer composition. For satisfying thiscontent in the entire copolymer composition, the content of polymerblock A contained in the branched copolymer is also preferably in therange of about 10 to 50% by weight, more preferably about 25 to 50% byweight and most preferably about 35 to 45% by weight. If the relativeproportion of the polymer block A of aromatic vinyl monomer is toosmall, the shear adhesion failure temperature is lowered. In contrast,if the relative proportion of the polymer block A is too large, the peeladhesion is reduced.

The molecular weight of the branched copolymer is not particularlylimited, but, it should appropriately be chosen so that the blockcopolymer composition of the present invention has a weight averagemolecular weight (Mw) of 10,000 to 500,000, preferably 50,000 to 250,000and more preferably 80,000 to 150,000, as expressed in terms of theweight average molecular weight converted by polystyrene standardmeasured by the gel permeation chromatography (GPC).

The content of the branched copolymer having at least four branches inthe aromatic vinyl compound-isoprene block copolymer composition of thepresent invention is in the range of 5 to 43.9% by weight based on thetotal weight of the block copolymer composition. If the content of thebranched copolymer with at least four branches is too small, the shearadhesion failure temperature is not sufficiently high. If the content ofthe branched copolymer is too large, the aromatic vinylcompound-isoprene block copolymer composition has an undesirably highviscosity and its proccessability is reduced. The content of thebranched copolymer with at least four branches is preferably in therange of 15 to 43.9% by weight and more preferably 25 to 43.9% byweight.

(2) Diblock copolymer

The second ingredient, i.e., the diblock copolymer of formula (II)contained in the block copolymer composition of the present invention isa straight chain diblock copolymer composed of the polymer block A′ ofaromatic vinyl monomer and the polymer block B of isoprene.

The aromatic vinyl monomer used for the preparation of the diblockcopolymer is not particularly limited, and includes, for example,styrene, α-methylstyrene, vinyltoluene and vinylnaphthalene. Of these,styrene is preferable. These aromatic vinyl monomers may be used eitheralone or as a combination of at least two thereof. As the aromatic vinylmonomer, the same monomer as that used for the preparation of thepolymer block A of the branched copolymer is usually used, but adifferent monomer may be used.

The proportion of the polymer block A′ of aromatic vinyl monomer in thediblock copolymer is not particularly limited, but, the content of thepolymer block of aromatic vinyl monomer in the aromatic vinylcompound-isoprene copolymer composition of the present invention is inthe range of 10 to 50% by weight, preferably 25 to 50% by weight andmore preferably 35 to 45% by weight, based on the total weight of theblock copolymer composition. For satisfying this content in the entirecopolymer composition, the content of polymer block A′ contained in thediblock copolymer is also preferably in the range of about 10 to 50% byweight, more preferably about 25 to 50% by weight and most preferablyabout 35 to 45% by weight. If the relative proportion of polymer blockA′ of aromatic vinyl monomer is too small, the shear adhesion failuretemperature is reduced. In contrast, if the relative proportion of thepolymer block A′ is too large, the peel adhesion is reduced.

The molecular weight of the diblock copolymer is not particularlylimited, but, it should appropriately be chosen so that the blockcopolymer composition of the present invention usually has a weightaverage molecular weight (Mw) of 3,000 to 250,000, preferably 15,000 to200,000 and more preferably 20,000 to 150,000, as expressed in terms ofthe weight average molecular weight converted by polystyrene standardmeasured by GPC.

The content of the diblock copolymer in the aromatic vinylcompound-isoprene block copolymer composition of the present inventionis in the range of 56.1 to 95% by weight based on the total weight ofthe block copolymer composition. If the content of the diblock copolymeris too small, the peel adhesion is reduced. In contrast, if the contentof the diblock copolymer is too large, the shear adhesion failuretemperature is not sufficiently high. The content of the diblockcopolymer is preferably in the range of 56.1 to 85% by weight and morepreferably 56.1 to 75% by weight.

(3) Other polymer

The aromatic vinyl compound-isoprene block copolymer of the presentinvention may comprise, in addition to the above-mentioned branchedcopolymer having at least four branches and the above-mentioned diblockcopolymer, a branched copolymer having two branches and a branchedcopolymer having three branches. That is, the block copolymercomposition of the present invention may comprise at least one optionalbranched copolymer selected from branched copolymers having two or threebranches which are represented by the following formula (III):

(A″-B)_(m)X  (III)

wherein A″ is a polymer block of an aromatic vinyl monomer, B is apolymer block of isoprene, X is a residue of a polyfunctional couplingagent, and m is an integer of 2 or 3. As specific examples of thearomatic vinyl monomer used for the polymer block A″, there can bementioned styrene, α-methylstyrene, vinyltoluene and vinylnaphthalene.Of these, styrene is preferable. These aromatic vinyl monomers may beused either alone or in combination.

However, the amount of the branched copolymer of formula (III) ispreferably minor. That is, in order to attain the desired high shearadhesion failure temperature, the sum of a branched copolymer having twobranches and a branched copolymer having three branches is preferablysmaller than the amount of the branched copolymer having at least fourbranches. Usually the sum of a branched copolymer having two branchesand a branched copolymer having three branches is not larger than 20% byweight, preferably not larger than 15% by weight, based on the weight ofthe aromatic vinyl compound-isoprene block copolymer.

(4) Physical Properties

The content of aromatic vinyl monomer units in the aromatic vinylcompound-isoprene copolymer is not particularly limited, and, forexample, is in the range of 10 to 50% by weight, preferably 25 to 50% byweight and more preferably 35 to 45% by weight, to obtain highlybalanced shear adhesion failure temperature and peel adhesion.

The molecular weight of the aromatic vinyl compound-isoprene copolymercomposition of the present invention is in the range of 10,000 to500,000, preferably 50,000 to 250,000 and more preferably 80,000 to150,000, as expressed in terms of the weight average molecular weightconverted by polystyrene standard measured by GPC. If the molecularweight of the copolymer composition is too low, the shear adhesionfailure temperature is lowered. In contrast, if the molecular weight ofthe copolymer composition is too high, the melt viscosity becomesundesirably high and the proccessability is reduced.

The molecular weight distribution of the aromatic vinylcompound-isoprene copolymer composition of the present invention is notparticularly limited, but, the ratio (Mw/Mn) of the weight averagemolecular weight (Mw) to the number average molecular weight (Mn), asexpressed in terms of the molecular weight converted by polystyrenestandard measured by GPC, is usually not larger than 4, preferably inthe range of 1.1 to 3 and more preferably 1.2 to 2.0 to obtain highlybalanced shear adhesion failure temperature and peel adhesion.

(5) Production process

The process for producing the aromatic vinyl compound-isoprene copolymercomposition of the present invention is not particularly limited, but,the aromatic vinyl compound-isoprene copolymer composition is preferablyproduced by preparing an A-B diblock copolymer having a structure suchthat a polymer block B composed of isoprene units and having a terminalexhibiting a polymerization activity is directly bonded to a polymerblock of aromatic vinyl monomer units; and then, coupling a part of theA-B diblock copolymer to give a block copolymer having at least fourbranches, whereby a composition comprising the block copolymer having atleast four branches and the diblock copolymer is obtained at one time.More specifically, the preferable process for producing the aromaticvinyl compound-isoprene block copolymer composition comprises the stepsof allowing an aromatic vinyl monomer to contact with an organic lithiuminitiator to prepare a polymer block A composed of aromatic vinylmonomer units and having an active terminal exhibiting a polymerizationactivity; incorporating isoprene to the polymer block A-containingpolymerization system to give an A-B block copolymer having a structuresuch that a polymer block B composed of isoprene units and having anactive terminal exhibiting a polymerization activity is directly bondedto the polymer block A of aromatic vinyl monomer units; and then, addinga coupling agent having at least four functionalities to the A-B blockcopolymer-containing polymerization system to convert 5 to 50% by weightof the A-B block copolymer to the branched polymer having at least fourbranches represented by the formula (I).

Alternatively, the aromatic vinyl compound-isoprene copolymercomposition can be produced by a process comprising the steps ofseparately preparing the branched block copolymer having at least fourbranches and the diblock copolymer, and then, mixing together thethus-prepared two block copolymers at a predetermined mixing ratio.

The steps in the preferable process for producing the aromatic vinylcompound-isoprene block copolymer composition will be described indetail.

(i) In the first step, an aromatic vinyl monomer is polymerized in apolymerization medium by using an organic lithium initiator. As theorganic lithium initiator, conventional initiators capable ofpolymerizing an aromatic vinyl monomer and isoprene are used. Asexamples of the organic lithium initiator, there can be mentionedorganic monolithium initiators such as methyllithium, n-propyllithium,n-butyllithium and sec-butyllithium. Of these, n-butyllithium ispreferable. The amount of the organic lithium initiator used can becalculated depending upon the intended molecular weight of the copolymerby the method well known to a person skilled in the art.

The polymerization medium used is not particularly limited provided thatit is inactive for the organic lithium initiator, and it includes, forexample, open chain hydrocarbon solvents, cyclic hydrocarbon solventsand mixtures thereof. As specific examples of the open chain hydrocarbonsolvents, there can be mentioned open chain alkanes and alkenes having 4to 6 carbon atoms such as n-butane, isobutane, n-hexane and theirmixtures; 1-butene, isobutylene, trans-2-butene, cis-2-butene and theirmixtures; 1-pentene, trans-2-pentene, cis-2-pentene and their mixtures;and n-pentane, isopentane, neopentane and their mixtures. As specificexamples of the cyclic hydrocarbon solvents, there can be mentionedaromatic hydrocarbons such as benzene, toluene and xylene, and alicyclichydrocarbons such as cyclohexane. With a view to controlling thepolymerization temperature, and the molecular weight distribution of thepolymer block of aromatic monomer and the aromatic vinylcompound-isoprene block copolymer composition, it is preferable to use amixed solvent composed of open chain hydrocarbon solvent having 4 to 6carbon atoms and a cyclic hydrocarbon solvent preferably at a ratio of5:95 to 40:60 by weight, more preferably 10:90 to 40:60 by weight.

In the present invention, the polymerization of an aromatic vinylmonomer can be conducted in the presence of a polar compound. By using apolar compound, the rate of polymerization and the molecular weightdistribution in the polymer block of aromatic vinyl monomer can becontrolled. The polar compound used preferably includes aromatic andaliphatic ethers and tertiary amines having a relative dielectricconstant of 2.5 to 5.0 at 25° C. As specific examples of such polarcompounds, there can be mentioned aromatic ethers such as diphenyl etherand anisole; aliphatic ethers such as diethyl ether and dibutyl ether;tertiary monoamines such as trimethylamine, triethylamine andtripropylamine; and tertiary polyamines such astetramethylethylenediamine and tetraethylethylenediamine. These polarcompounds may be used either alone or as a combination of at least twothereof. The amount of the polar compound used is preferably in therange of 0.001 to 50 moles, more preferably 0.005 to 10 moles, per moleof the organic lithium initiator.

The procedure by which an aromatic vinyl monomer is polymerized is notparticularly limited, and any of the conventional procedures can beemployed. For example, a batch polymerization procedure wherein theentire amount of the aromatic vinyl monomer and the entire amount of theinitiator are charged at one time in the polymerization system to effectpolymerization; a continuous polymerization procedure wherein thearomatic vinyl monomer and the initiator are continuously incorporatedin the polymerization system; and a polymerization procedure wherein apart of the aromatic vinyl monomer and a part of the initiator arecharged to conduct polymerization until a predetermined conversion isreached, and then, the remainders of the monomer and initiator are addedto continue polymerization can be employed. The polymerizationtemperature is usually in the range of 0° C. to 90° C., preferably 20°C. to 80° C. In the case where the reaction temperature is difficult tocontrol, reflux cooling is preferably conducted by using a reactorequipped with a reflux condenser.

(ii) In the second step, isoprene is incorporated into thepolymerization system comprising the thus-produced polymer block A ofaromatic vinyl monomer having an active terminal exhibiting apolymerization activity to effect polymerization of isoprene to give anA-B block copolymer having a structure such that a polymer block Bcomposed of isoprene units and having an active terminal exhibiting apolymerization activity is directly bonded to the polymer block A ofaromatic vinyl monomer units. The incorporation of isoprene can becarried out continuously to control the heat of reaction.

(iii) After the completion of polymerization of isoprene, apolyfunctional coupling agent having at least four functionalities isincorporated in the polymerization system whereby the A-B blockcopolymer having an active terminal is bonded to each other to give theblock copolymer having at least four branches represented by formula(I). A compound capable of accelerating the coupling reaction can beadded, if desired.

To obtain the block copolymer having at least four branches, a couplingagent capable of providing at least four sites capable of reacting withthe active terminals exhibiting a polymerization activity must be used.As examples of the coupling agent, there can be mentioned silanecompounds such as halogenated silanes and alkoxysilanes; tin compoundssuch as tin halides; polycarboxylic acid esters; epoxy compounds such asepoxidized soybean oil; acrylic acid esters such as pentaerythritoltetraacrylate; epoxysilanes; and divinyl compounds such asdivinylbenzene. Of these, tetrafunctional coupling agents arepreferable, and, as specific examples thereof, there can be mentionedtetrachlorosilane, tetrabromosiane, tetramethoxysilane,tetraethoxysilane, tetrachlorotin and diethyl adipate. Provided that theobject of the invention is achieved, these coupling agents can be usedeither alone or as a combination of at least thereof. These couplingagents may be used in combination with bi- or tri-functional couplingagents.

The amount of the coupling agent used in the present invention isimportant, and should appropriately be chosen so that the branchedcopolymer having at least four branches and the diblock copolymer areproduced at the predetermined ratio, although the optimum ratio variesdepending upon the particular kind of coupling agent. The amount of thecoupling agent is usually in the range of 0.001 to 0.2 mole, preferably0.01 to 0.15 mole and more preferably 0.02 to 0.12 mole per mole of theorganic lithium initiator. By using this amount of the coupling agent,the branched copolymer having at least four branches is produced in anamount of 5 to 50% by weight, preferably 15 to 50% by weight and morepreferably 25 to 45% by weight, based on the total weight of the blockcopolymer composition. If the amount of the coupling agent is too large,a block copolymer having two branches and represented by the formula(A-B)₂X, a block copolymer having three branches and represented by theformula (A-B)₃X and a straight chain block copolymer having a residue ofthe coupling agent at a terminal and represented by the formula A-B-Xare produced in large amounts (in these formulae, A, B and X are asdefined above), and only a minor amount of the branched copolymer havingat least four branches is produced.

An appropriate amount of the coupling agent can be determined bycalculation depending upon the compositions of the branched copolymerand the diblock copolymer in the intended block copolymer composition.Actually, deactivation of the organic lithium initiator and the couplingagent, and other factors must be considered, and thus, the optimumamount thereof is preferably determined by conducting preliminaryexperiments. According to the need, a reaction stopper such as methanolcan be used to control the coupling percentage.

(iv) After the completion of coupling, a reaction stopper such as water,an alcohol or an acid is added to deactivate the polymerization activesites. An antioxidant is added to the polymerization product, and then,a polymer is separated by a conventional procedure, for example, a steamstripping procedure, followed by drying, whereby the aromatic vinylcompound-isoprene block copolymer composition of the present inventioncomprising the branched copolymer having at least four branches and anuncoupled copolymer, i.e., the diblock copolymer, is obtained.

As mentioned above, it is possible that the diblock copolymer of formula(A′-B) is prepared separately from the branched copolymer having atleast four branches, and then, the diblock copolymer is mixed togetherwith the branched copolymer having at least four branches. The diblockcopolymer can be prepared by a process wherein a straight chain (A′-B)diblock copolymer having a structure such that a polymer block B ofisoprene having an active terminal exhibiting a polymerization activityis directly bonded to a polymer block A′ of aromatic vinyl monomer isprepared in a manner similar to the above-mentioned steps (i) and (ii);and the polymerization active sites are deactivated, an antioxidant isadded, and then, the (A′-B) diblock copolymer is separated and driedwithout subjected to a coupling reaction in a manner similar to theabove-mentioned step (iv).

Adhesive or Pressure Sensitive Adhesive composition

The adhesive or pressure sensitive adhesive composition of the presentinvention comprises the above-mentioned aromatic vinyl compound-isopreneblock copolymer composition and a tackifier.

In the adhesive or pressure sensitive adhesive composition of thepresent invention, rubber ingredients can be incorporated provided thatthe intended adhesive properties are obtained, which ingredientsinclude, for example, styrene block copolymers such as astyrene-butadiene-styrene block copolymer, astyrene-ethylene-butylene-styrene block copolymer and astyrene-ethylene-propylene-styrene block copolymer; diene polymerrubbers such as butadiene rubber and isoprene rubber; and naturalrubber.

The tackifier used in the present invention is not particularly limited,and includes, for example, natural resin and synthetic resin tackifierswhich are known and conventionally used in general adhesivecompositions. The natural resin tackifier includes rosin type resins andterpene type resins. As specific examples of the rosin type resins,there can be mentioned rosins such as gum rosin, tall rosin and woodrosin; modified rosins such as hydrogenated rosin, disproportionatedrosin and polymerized rosin; and esters such as glycerol ester andpentaerythritol esters, of these rosins and modified rosins. As specificexamples of the terpene type resins, there can be mentioned terpeneresins such as α-pinene, β-pinene and dipentene (limonene); aromaticmodified terpene resins; hydrogenated terpene resins; and terpene-phenolresins. The synthetic resin tackifier includes a polymerized type and acondensed type. As specific examples of the polymerized type resin,there can be mentioned petroleum resins such as aliphatic (C₅)petroleumresins, aromatic (C₉)petroleum resins, copolymerized (C₅/C₉) petroleumresins, hydrogenated petroleum resins (alicyclic petroleum resins), DCPDand other alicyclic petroleum resins; cumarone-indene resins; andpure-monomer petroleum resins such as styrene resins and substitutedstyrene resins. As specific examples of the condensed type resins, therecan be mentioned phenol resins such as alkyl phenol resins androsin-modified phenol resins, and xylene resins. Of these, petroleumresins, especially alicyclic petroleum resins are preferable.

The tackifier can be used either alone or as a combination of at leasttwo thereof. The amount of the tackifier is usually in the range of 10to 500 parts by weight, preferably 50 to 350 parts by weight and morepreferably 70 to 250 parts by weight, based on 100 parts by weight ofthe aromatic vinyl compound-isoprene block copolymer composition.

In the adhesive or pressure sensitive adhesive composition of thepresent invention, if desired, rubber ingredients can be incorporatedprovided, which include, for example, styrene block copolymers such as astyrene-butadiene-styrene block copolymer, astyrene-ethylene-butylene-styrene block copolymer and astyrene-ethylene-propylene-styrene block copolymer; diene polymerrubbers such as butadiene rubber and isoprene rubber; and naturalrubber. Additives can also be incorporated, which include, for example,a softening agent (plasticizer), an antioxidant, a heat stabilizer, anultraviolet absorber and a filler.

The softening agent includes those which are known and conventionallyused for adhesive or pressure sensitive adhesive compositions, such asaromatic, paraffinic and naphthenic extender oils, and liquid polymers,for example, polybutene and polyisobutylene. Of these, paraffinic andnaphthenic extender oils are preferable. The amount of the softeningagent is usually in the range of 10 to 500 parts by weight, preferably20 to 300 parts by weight and more preferably 30 to 150 parts by weight,based on 100 parts by weight of the aromatic vinyl compound-isopreneblock copolymer composition because good viscosity characteristics areobtained and undesirable bleeding can be minimized.

As specific examples of the antioxidant, there can be mentioned hinderedphenol compounds such as 2,6-di-tert.-butyl-p-cresol, pentaerythrityltetrakis[3-(3,5-di-tert.-butyl-4-hydroxyphenyl)propionate] and2,4-bis-(n-octylthio)-6-(4-hydroxy-3,5-di-tert.-butylanilino)-1,3,5-triazine;thiodicarboxylate esters such as dilauryl thiodipropionate; andphosphate salts such as tris(nonylphenyl) phosphate,4,4′-butylidene-bis(3-methyl-6-tert.-butylphenyl)-ditridecyl phosphate.These antioxidants may be used either alone or in combination.

The adhesive or pressure sensitive adhesive composition of the presentinvention can be used as a solvent type adhesive or pressure sensitiveadhesive composition dissolved in a solvent such as n-hexane,cyclohexane, benzene and toluene; an emulsion type adhesive or pressuresensitive adhesive composition, which is an aqueous emulsion prepared bydispersing in water by using an emulsifier; or a hot-melt type adhesiveor pressure sensitive adhesive composition which contains no solvent.Especially the adhesive or pressure sensitive adhesive composition issuitable for a hot-melt adhesive.

The hot melt adhesive is especially suitable for making disposable goodssuch as disposable diapers, sanitary napkins, hospital gowns, bed padsand surgery drapes; and for use as constructive adhesive, elasticadhesives, and other uses. It also is suitable for making pressuresensitive adhesive tapes, labels, books and assemblies. The pressuresensitive adhesive tapes include a broad range of tapes such as thosewhich are used for packaging tapes, office stationery, double coatedtapes, masking tapes and electrical insulation tapes. The adhesive orpressure sensitive adhesive composition exhibits a high peel adhesion.It further exhibits a low viscosity no matter how it is applied as asolvent adhesive or a hot melt adhesive, and thus, it has goodproccessability for coating. When the adhesive or pressure sensitiveadhesive composition is used for making labels, it exhibits lowviscosity and high peel adhesion, and thus, the proccessability forcoating and adhesion characteristics are satisfactory, and further, thecoated sheet exhibits good die-cuttability.

The invention will now be described by the following working examples.In the examples and comparative examples, parts and % are by weightunless otherwise specified.

In the working examples, molecular weights of polymers were determinedby a high performance liquid chromatography using tetrahydrofuran as acarrier and expressed in terms of a weight average molecular weight (Mw)converted by polystyrene standard. The amount of respective ingredientsin the copolymer composition was calculated from the area of peak asobtained by a high performance liquid chromatography.

EXAMPLE 1 Preparation of Block Copolymer Composition

A 50 liter pressure-resistant reactor was charged with 18.75 kg of amixed solvent composed of 30% n-butane/70% cyclohexane, 240 milli-moleof dibutyl ether (relative dielectric constant: 3.06 at 25° C.) and 230milli-mole of n-butyl lithium as an initiator. Then 3.04 kg of styrenewas incorporated in the reactor to conduct polymerization at 30° C. forone hour, and then, 4.96 kg of isoprene was added to conductpolymerization for about 1.5 hours while the reaction temperature wascontrolled to fall between 50° C. and 60° C. by reflux cooling. Then 25milli-mole of tetramethoxysilane as a coupling agent was added toconduct a coupling reaction for 2 hours. Thereafter, 50 ml of methanolas a polymerization stopper and 40 g of 2,6-di-tert. -butyl-p-cresolwere added and the mixture was thoroughly mixed together. Then the mixedsolution was gradually added dropwise to hot water maintained at atemperature of 85 to 95° C. to evaporate off the solvent from thesolution. The thus-obtained polymer was subjected to pulverization andhot-air drying to give a block copolymer composition. The blockcopolymer composition had a styrene content of 38% by weight, a weightaverage molecular weight (Mw) of 96,000 as expressed in terms of that ofpolystyrene, and a molecular weight distribution (Mw/Mn) of 1.43. Thecopolymer composition was composed of 35.3% of a branched copolymerhaving four branches, 4.7% of a branched copolymer having threebranches, 1.2% of a branched copolymer having two branches and 58.8% ofa diblock copolymer.

Adhesive Composition

A kneader having stirring blades was charged with 30 parts by weight ofthe above-mentioned block copolymer composition, and then, 50 parts of atackifier “Alkon M-100” supplied by Arakawa Chem. Ind. Co.), 20 parts ofnaphthenic process oil (“Shellflex 371” supplied by Shell Chem. Co.) and0.2 part of an antioxidant (“Irganox 1010” supplied Ciba-Geigy Co.) wereadded. After the atmosphere in the kneading system was substituted withnitrogen, kneading was conducted at a temperature of 160 to 180° C. toprepare an adhesive or pressure sensitive adhesive composition. The meltviscosity of the adhesive or pressure sensitive adhesive composition wasmeasured at 150° C. by using a Brookfield thermogel viscometer. Apolyester film having a thickness of 30 μm was coated with the adhesiveor pressure sensitive adhesive composition to a thickness of 30 μm, andadhesive properties of the adhesive coating were evaluated.

Evaluation of Adhesive Properties

The peel adhesion (N/m) was evaluated according to PSTC-1 (Peel adhesiontest at 180° angle issued by Pressure Sensitive Tape Council, U.S.A.) byusing stainless steel or polyethylene as an adherend material.

The shear adhesion failure temperature (° C.) was measured by usingstainless steel as an adherend material at an adhered area of 10×25 mm,a load of 1 kg and a temperature elevation rate of 0.5° C./min. Theevaluation results are shown in Table 1.

EXAMPLES 2 to 5 Comparative Examples 1 to 7

Block copolymer compositions were prepared and their characteristicswere evaluated, and adhesive compositions were prepared from the blockcopolymer compositions and their adhesive properties were evaluated, bysubstantially the same procedures as described in Example 1, whereintetrachlorosilane (TCS) was used instead of tetramethoxysilane (TMS) asa coupling agent and the amount of the coupling agent was varied asshown in Tables 1 and 2 in Examples 2 and 3, and Comparative Example 1;phenyl-trichorsilane (PTCS) was used instead of TMS as a coupling agentand the amount of the coupling agent was varied as shown in Table 2 inComparative Example 2; and the amount of tetramethoxysilane (TMS) wasvaried as shown in Tables 1 and 2 in Examples 4 and 5, and ComparativeExample 3. The evaluation results are shown in Tables 1 and 2.

In Comparative Example 4, a block copolymer composition was prepared bya process described in U.S. Pat. No. 5,394,627 wherein, after completionof polymerization of isoprene, 1.2% by weight, based on the weight ofisoprene, of butadiene was added and tetrachlorosilane in an amountshown in Table 2 was reacted with all other conditions remaining thesame as in Example 1. The characteristics of the block copolymercomposition were evaluated, and an adhesive or pressure sensitiveadhesive composition was prepared from the block copolymer compositionand the adhesive properties of the adhesive or pressure sensitiveadhesive composition were evaluated, by the same procedures as inExample 1. The evaluation results are shown in Table 2.

In Comparative Examples 5, 6 and 7, the following commercially availablestyrene-isoprene-styrene block copolymer compositions A, B and C wereused, respectively. Their characteristics were evaluated, and adhesivecompositions were prepared from the block copolymers and their adhesiveproperties were evaluated, by the same procedures as in Example 1. Theevaluation results are shown in Table 2.

Commercially available block copolymer composition A: “Kraton D1124P”supplied by Shell Co.

Commercially available block copolymer composition B: “Vector 4211”supplied by Dexco Co.

Commercially available block copolymer composition C: “Vector 4411”supplied by Dexco Co.

The abbreviations for coupling agents occurring in Tables 1 and 2 are asfollows.

TMS: tetramethoxysilane

TCS: tetrachlorosilane

PTCS: phenyltrichlorosilane

TABLE 1 Example 1 2 3 4 5 Coupling agent TMS TCS TCS TMS TMS Couplingagent/initiator mol ratio 0.11 0.07 0.09 0.05 0.12 Block copolymerStyrene content (%) 38 41 37 37 31 Mw of copolymer composition (×1,000)96 98 116 74 135 Molecular weight distribution (Mw/Mn) 1.43 1.36 1.391.29 1.46 Composition of copolymer composition (%) Diblock copolymer58.8 72.5 64.5 80.6 56.1 Copolymer with 2 branches 1.2 0 0 0 1.7Copolymer with 3 branches 4.7 0.8 1.0 1.7 7.3 Copolymer with 4 branches35.3 26.7 34.5 17.7 34.9 Melt viscosity of adhesive composition 1,9303,700 3,800 1,060 4,500 (150° C., cps) Peel adhesion (N/m) to steel1,170 1,250 1,200 1,150 1,120 to polyethylene 530 550 570 560 550 Shearadhesion failure temperature (° C.) 71 70 70 68 68

TABLE 2 Comparative Example 1 2 3 4 5 6 7 Coupling agent TCS PTCS TMSTCS — — — Coupling agent/initiator mol ratio 0.18 0.12 0.21 0.25 — — —Block copolymer A B C Styrene content (%) 38 36 31 37 30 29 44 Mw ofcopolymer composition (×1,000) 107.6 92 151 125 145 120 90 Molecularweight distribution (Mw/Mn) 1.55 1.30 1.38 1.39 1.52 1.02 1.05Composition of copolymer composition (%) Diblock copolymer 34.2 66.523.9 8.0 27.6 0 0 Copolymer with 2 branches 2.9 2.4 14.4 0 4.6 100 100Copolymer with 3 branches 28.2 31.4 51.7 22.0 67.8 0 0 Copolymer with 4branches 34.7 0 10.0 70.0 0 0 0 Melt viscosity of adhesive composition1,870 2,050 17,500 3,800 9,200 6,700 4,200 (150° C., cps) Peel adhesion(N/m) to steel 960 1,050 940 920 950 970 960 to polyethylene 490 520 480470 500 460 470 Shear adhesion failure temperature (° C.) 70 65 72 68 7163 70

Industrial Applicability

The aromatic vinyl compound-isoprene block copolymer composition of thepresent invention is useful for a hot-melt adhesive composition, andother adhesive or pressure sensitive adhesive compositions. An adhesiveor pressure sensitive adhesive composition made from the block copolymercomposition of the present invention has a low-melt-viscosity andlow-application-temperature and exhibits high and balanced peel adhesionand shear adhesion failure temperature.

A hot-melt adhesive made from the block copolymer composition of thepresent invention satisfy the following characteristics.

Melt viscosity at 150° C.: not larger than 5,000 cps

Shear adhesion failure temperature: at least 66° C.

Peel adhesion to steel: at least 1,000 N/m

Peel adhesion to polyethylene: at least 500 N/m

What is claimed is:
 1. An aromatic vinyl compound-isoprene blockcopolymer composition comprising: (i) 5 to 43.9% by weight of a branchedcopolymer having at least four branches, represented by the followinggeneral formula (I): (A-B)_(n)X  (I) wherein A is a polymer block of anaromatic vinyl monomer, B is a polymer block of isoprene, X is a residueof a polyfunctional coupling agent having at least four functionalities,and n is an integer of at least 4, (ii) 56.1 to 95% by weight of adiblock copolymer represented by the following general formula (II):A′-B  (II) wherein A′ is a polymer block of an aromatic vinyl monomer,which may be the same as or different from the polymer block A, and B isa polymer block of isoprene, and (iii) at least one branched copolymerselected from the group consisting of branched copolymers having twobranches and branched copolymers having three branches, which arerepresented by the following general formula (III): (A″-B)_(m)X  (III)wherein A″ is a polymer block of an aromatic vinyl monomer, B is apolymer block of isoprene, X is a residue of a polyfunctional couplingagent, and m is an integer of 2 or 3; the amount of the branchedcopolymer of formula (III) being smaller than the amount of the branchedcopolymer of formula (I); said block copolymer composition having aweight average molecular weight of 10,000 to 500,000.
 2. The aromaticvinyl compound-isoprene block copolymer composition according to claim1, wherein the aromatic vinyl monomer constituting the polymer block Aof the branched copolymer represented by formula (I) is at least onemonomer selected from styrene, α-methylstyrene, vinyltoluene andvinylnaphthalene.
 3. The aromatic vinyl compound-isoprene blockcopolymer composition according to claim 1, wherein the content of thepolymer block A of the aromatic vinyl monomer in the branched copolymerrepresented by formula (I) is in the range of 10 to 50% by weight basedon the weight of the branched copolymer represented by formula (I). 4.The aromatic vinyl compound-isoprene block copolymer compositionaccording to claim 1, wherein the aromatic vinyl monomer constitutingthe polymer block A′ of the diblock copolymer represented by formula(II) is at least one monomer selected from styrene, α-methylstyrene,vinyltoluene and vinylnaphthalene.
 5. The aromatic vinylcompound-isoprene block copolymer composition according to claim 1,wherein the content of the polymer block A′ of the aromatic vinylmonomer in the diblock copolymer of formula (II) is in the range of 10to 50% by weight based on the weight of the branched copolymer.
 6. Thearomatic vinyl compound-isoprene block copolymer composition accordingto claim 1, wherein the content of the branched copolymer of formula(III) is not larger than 20% by weight based on the weight of thearomatic vinyl compound-isoprene block copolymer composition.
 7. Thearomatic vinyl compound-isoprene block copolymer composition accordingto claim 1, wherein the ratio (Mw/Mn) of the weight average molecularweight (Mw) to the number average molecular weight (Mn) is not largerthan
 4. 8. A process for producing an aromatic vinyl compound-isopreneblock copolymer composition comprising: (i) 5 to 43.9% by weight of abranched copolymer having at least four branches, represented by thefollowing general formula (I): (A-B)_(n)X  (I) wherein A is a polymerblock of an aromatic vinyl monomer, B is a polymer block of isoprene, Xis a residue of a polyfunctional coupling agent having at least fourfunctionalities, and n is an integer of at least 4, (ii) 56.1 to 95% byweight of a diblock copolymer represented by the following generalformula (II′): A-B  (II′) wherein A is a polymer block of an aromaticvinyl monomer, and B is a polymer block of isoprene, and (iii) at leastone branched copolymer selected from the group consisting of branchedcopolymers having two branches and branched copolymers having threebranches, which are represented by the following general formula (III):(A″-B)_(m)X  (III) wherein A″ is a polymer block of an aromatic vinylmonomer, B is a polymer block of isoprene, X is a residue of apolyfunctional coupling agent, and m is an integer of 2 or 3; the amountof the branched copolymer of formula (III) being smaller than the amountof the branched copolymer of formula (I); said block copolymercomposition having a weight average molecular weight of 10,000 to500,000, which comprises the steps of: allowing an aromatic vinylmonomer to contact with an organic lithium initiator to prepare apolymer block A composed of aromatic vinyl monomer units and having anactive terminal exhibiting a polymerization activity; incorporatingisoprene to the polymer block A-containing polymerization system wherebyan A-B block copolymer is prepared, which has a structure such that thepolymer block A of aromatic vinyl monomer is directly bonded to apolymer block B composed of isoprene units and having an active terminalexhibiting a polymerization activity; and then, adding a coupling agenthaving at least four functionalities to the A-B blockcopolymer-containing polymerization system to convert 5 to 43.9% byweight of the A-B block copolymer to a branched copolymer having atleast four branches represented by formula (I).
 9. The process forproducing an aromatic vinyl compound-isoprene block copolymercomposition according to claim 8, wherein the organic lithium initiatoris n-butyllithium.
 10. The process for producing an aromatic vinylcompound-isoprene block copolymer composition according to claim 8,wherein the polymerization reactions are conducted in a polymerizationmedium which is a mixed solvent composed of 5 to 50% by weight of anopen chain hydrocarbon solvent having 4 to 6 carbon atoms and 95 to 50%by weight of at least one cyclic hydrocarbon solvent selected fromalicyclic hydrocarbons and aromatic hydrocarbons.
 11. The process forproducing an aromatic vinyl compound-isoprene block copolymercomposition according to claim 8, wherein the aromatic vinyl monomer isat least one monomer selected from styrene, α-methylstyrene,vinyltoluene and vinylnaphthalene.
 12. The process for producing anaromatic vinyl compound-isoprene block copolymer composition accordingto claim 1, wherein the amounts of the aromatic vinyl monomer andisoprene are in the ranges of 10 to 50% by weight and 90 to 50% byweight, respectively, based on the total weight of these two monomers.13. The process for producing an aromatic vinyl compound-isoprene blockcopolymer composition according to claim 8, wherein the polymerizationof the aromatic vinyl monomer is conducted in the presence of a polarcompound.
 14. The process for producing an aromatic vinylcompound-isoprene block copolymer composition according to claim 13,wherein the polar compound is at least one compound selected fromaromatic and aliphatic ethers, and tertiary amines, which have arelative dielectric constant of 2.5 to 5.0 at 25° C.
 15. The process forproducing an aromatic vinyl compound-isoprene block copolymercomposition according to claim 8, wherein the amount of the couplingagent used is in the range of 0.001 to 0.2 mole per mole of the organiclithium initiator.
 16. An adhesive or pressure sensitive adhesivecomposition comprising an aromatic vinyl compound-isoprene blockcopolymer composition and a tackifier, characterized in that saidaromatic vinyl compound-isoprene block copolymer composition comprises:(i) 5 to 43.9% by weight of a branched copolymer having at least fourbranches, represented by the following general formula (I):(A-B)_(n)X  (I) wherein A is a polymer block of an aromatic vinylmonomer, B is a polymer block of isoprene, X is a residue of apolyfunctional coupling agent having at least four functionalities, andn is an integer of at least 4, and (ii) 56.1 to 95% by weight of adiblock copolymer represented by the following general formula (II):A′-B  (II) wherein A′ is a polymer block of an aromatic vinyl monomer,which may be the same as or different from the polymer block A, and B isa polymer block of isoprene, and (iii) at least one branched copolymerselected from the group consisting of branched copolymers having twobranches and branched copolymers having three branches, which arerepresented by the following general formula (III): (A″-B)_(m)X  (III)wherein A″ is a polymer block of an aromatic vinyl monomer, B is apolymer block of isoprene, X is a residue of a polyfunctional couplingagent, and m is an integer of 2 or 3; the amount of the branchedcopolymer of formula (III) being smaller than the amount of the branchedcopolymer of formula (I); said block copolymer composition having aweight average molecular weight of 10,000 to 500,000.
 17. The adhesiveor pressure sensitive adhesive composition according to claim 16,wherein the content of the tackifier is in the range of 10 to 500 partsby weight based on 100 parts by weight of the aromatic vinylcompound-isoprene block copolymer composition.
 18. The adhesive orpressure sensitive adhesive composition according to claim 16, whereinthe aromatic vinyl monomer constituting the polymer block A in thebranched copolymer of formula (I) and the aromatic vinyl monomerconstituting the polymer block A′ in the diblock copolymer of formula(II) are at least one monomer selected from styrene, α-methylstyrene,vinyltoluene and vinylnaphthalene.
 19. The adhesive or pressuresensitive adhesive composition according to claim 16, wherein thecontent of the polymer block A of the aromatic vinyl monomer in thebranched copolymer represented by formula (I) is in the range of 10 to50% by weight based on the weight of the branched copolymer, and thecontent of the polymer block A′ of the aromatic vinyl monomer in thediblock copolymer of formula (II) is in the range of 10 to 50% by weightbased on the weight of the diblock copolymer.